RU2192476C2 - Method of production of hot reducing gas for reduction of metal ore and plant for realization of this method - Google Patents

Abstract

FIELD: method of production of CO- and H₂- containing reducing gas used for reduction of finely-dispersed metal ores, iron ore in particular. SUBSTANCE: proposed method includes formation of reducing gas in gasifying zone through gasifying of carbon carriers , coal in particular at delivery of oxygen followed by cooling to temperature of reducing gas favorable for reduction process with no change of H₂O and/or CO₂ in it. To avoid Buduar reaction and heterogeneous water-and-gas reaction and consequently heating of reducing gas; reducing gas is converted into reducing gas of higher stability at reducing temperature due to introduction of H₂O and/or CO₂, which makes it possible to obtain gas in temperature range suitable for reduction of metal ore , i. e. below temperature at which melting and clogging are likely to occur and to eliminate chemical action on metal materials of gas carrying systems. EFFECT: enhanced efficiency. 9 cl, 1 dwg

Description

The invention relates to a method for producing a reducing gas containing CO and H ₂ , which serves to recover finely dispersed metal ore, in particular iron ore, in which the reducing gas is formed in the gasification zone by gasification of carbon carriers, in particular coal, by supplying oxygen, which is then cooled to a temperature of the reducing gas, suitable for the recovery process, and to the installation for implementing this method.

A method of the type described above is known, for example, from EP-A-0594557. In this known method, pig iron or semi-finished steel is formed in the melting gasification zone by smelting from at least partially reduced sponge iron by supplying carbon carriers and oxygen-containing gas, and a reducing gas containing CO and H _{2 is} produced. The reducing gas formed in the melting gasification zone has a temperature in the range of 1000-1200 ^o C. At this temperature, the released hydrocarbon compounds decompose. In addition, at such temperatures, the content of CO ₂ and H ₂ O drops below 6% for CO ₂ and below 4% for H ₂ O, since they are converted to CO and H ₂ .

In order to be used in a reduction reactor, this very hot reducing gas must be cooled before entering the reduction reactor. For example, according to EP-A-0594557, a nozzle cooler is used for this purpose. A portion of the reducing gas thus cooled is added to the reducing gas leaving the smelting gasification zone. Such traditional cooling of the reducing gas to ~ 700-900 ^° C, which is carried out by means of a cooled reducing gas of the same type, prevents the onset melting of ore particles in the reduction zone during ore reduction, but does not reduce the reducing potential of the reducing gas.

 The disadvantage is that the reducing gas so cooled is thermodynamically unstable; carbon monoxide and carbon are formed from carbon monoxide in accordance with the Boudoir equilibrium, just as in accordance with a heterogeneous water-gas equilibrium, carbon monoxide reacts with hydrogen to form water and carbon, which is exothermic, just like the first reaction. This leads to an increase in the temperature of the reducing gas and, consequently, the temperature of the material in the reactor, where the formation of agglomerates begins. Thus, the effect is not only on the recovery process, but also on the production of material in the recovery zone.

US-A-5185032 describes a method in which the hot reducing gas generated in a smelting-gasification apparatus is cooled to a temperature of ~ 900-950 ^{° C.} by injection of water.

FR-A-2236951 describes a method in which hot reducing gas generated in an electric furnace is supplied to a reduction shaft furnace located directly above the electric furnace, and after entering the reduction shaft furnace, it is cooled by injecting water, water vapor, carbon dioxide, hydrocarbons or another cooling medium to prevent agglomeration of particles of the metal oxide-containing material in the reduction shaft furnace. In the thus cooled reducing gas, the CO ₂ content in H ₂ O is relatively high.

 FR-A-766167 describes a method in which hot reducing gas generated in a smelting unit is supplied directly to the reducing chamber, while it is cooled in the dome region of the melting unit, that is, before being fed into the reducing chamber. Cooling is carried out either by supplying the spent reducing gas after removal of carbon dioxide, or by supplying a mixture of carbon dioxide or water vapor and coal in order to prevent agglomeration of the feed material in the reduction chamber.

The invention is aimed at eliminating these drawbacks and difficulties and has the task of creating a method of the type described above and an apparatus for implementing this method, providing a reducing gas in a temperature range suitable for reducing metal ore, that is, below a temperature at which melting and clogging phenomena can begin in at least partially reduced metal ore. Moreover, the content of H ₂ O / CO ₂ in the reducing gas should be optimized and the chemical effect on the metal materials of gas-bearing systems, i.e. reactors and gas transmission pipelines, embedded structures, etc., should be eliminated.

In the method of the type described, this problem is solved due to the fact that by introducing H ₂ O and / or CO ₂ - to prevent the Boudoir reaction and a heterogeneous water-gas reaction and, therefore, heating the reducing gas and metal ore - a reducing gas subjected to cooling without changing the content in it, H ₂ O / CO ₂ is converted into a reducing gas, thermodynamically more stable at a reducing temperature.

By selectively introducing H ₂ O and / or CO _{2, the} thermodynamically determined decomposition of CO and H ₂ reducing agents is selectively controlled or prevented. In the reducing gas, concentration ranges are regulated in which the Boudoir reaction and the heterogeneous water-gas reaction, which are highly exothermic, are suppressed so that an undesirable increase in the temperature of the reducing gas is eliminated. At the same time, using this method, the oxidation state of the reducing gas is controlled and the chemical effect on the metal structural elements is suppressed.

An advantage is that H ₂ O and / or CO ₂ is introduced in amounts ensuring an almost complete Boudoir equilibrium and a heterogeneous water-gas equilibrium of the reducing gas at a temperature suitable for the reduction process.

 The cooling of the reducing gas is preferably carried out by supplying a cooling gas of the same type and / or blast furnace gas.

The input of H ₂ About it is advisable to carry out by supplying water vapor, and the input of CO ₂ by supplying a gas containing CO ₂ .

In accordance with a preferred embodiment of the invention, the supply of CO ₂ to the reducing gas can be at least partially due to the fact that the reducing gas that has reacted during the reduction process, the so-called blast furnace gas, is supplied to the reducing gas. Other gases containing CO ₂ can also be used, for example CO ₂ purification products.

In order to provide intensive cooling of the reducing gas, it is preferably mixed with a cooled reducing gas of the same type as is known per se, and H ₂ O and / or CO ₂ are introduced into the cooled reducing gas of the same type.

Installation for implementing the method, including at least one recovery reactor with transport pipelines for metal ore and reducing gas included in it, a gasification reactor with feed pipelines for carbon and oxygen-containing gas carriers entering and a reducing gas outlet from it, as well as including cooling means placed in the pipeline of the reducing gas and not increasing the content of H ₂ O / CO ₂ in the reducing gas differs in We note that the source of CO ₂ and the source of H ₂ O are connected (connected) downstream to the chilled reducing gas supply pipe.

 It is advisable to equip the reduction reactor with a blast furnace gas outlet pipe to discharge the reacted reduction gas. A lateral pipeline is branched from it, connected downstream to the reducing gas pipeline.

Another preferred embodiment is characterized in that a recovery gas recirculation pipe is led out of the reducing gas pipeline, which is again connected through the scrubber and compressor to the reducing gas pipe at a point located above the branch point of the recovery gas recirculation pipe, relative to the flow direction of the reducing gas, in particular above the dedusting device available in the reducing gas pipeline and that the source O ₂ and H ₂ O source is connected with recirculation piping the reducing gas. The recovery reactor may be a reactor including a stationary fluidized bed, a venturi fluidized bed, a circulating fluidized bed or a cascade of cyclones.

 The invention will now be described in more detail with reference to the exemplary embodiment shown in the drawing, which schematically depicts a preferred construction of the installation according to the invention.

Reference numeral 1 denotes a preheating reactor made in the form of a preheating reactor with a fluidized bed 2, into which loading substances consisting of iron ore and fluxes can be fed through the loading pipe 3. The feed line 3 enters the reactor laterally at the level of the zone of the fluidized bed 2 (preheating zone). The gases generated in the reactor 1 by the fluidized bed and passing through it are discharged from it in the upper part through a gas outlet pipe 6 equipped with a gas purification cyclone 4 and a gas scrubber 5, such as a Venturi scrubber. In the form of a high-quality export gas with a calorific value of about 8000 kJ / Nm ^3, these gases can be used for various needs, for example, the production of electricity with or without oxygen production.

 Through the transport pipeline 7, the feed materials heated in the preheating reactor 1 with a fluidized bed are transferred to a reducing reactor 8, also made in the form of a fluidized bed reactor or a cascade of fluidized beds, and most of them are completely restored in this reactor.

 Through the transport pipeline of sponge iron 9 (for example, including a gas injector), the reduction products formed in the recovery reactor with a fluidized bed 8 are transferred to a melting-gasification apparatus 10; more precisely, they are introduced into it at the level of the carbon-containing layer present in the melting-gasification apparatus, in particular, above this layer or directly into it. The smelting and gasification apparatus contains at least one feeder 11 for coal and fluxes and nozzle feeders 12 for oxygen-containing gases located at several levels of height.

 Inside the melting gasification apparatus 10 below the melting gasification zone, molten pig iron 13 and molten slag 14 are collected, which can be diverted via separate outlets 15, 16. In the melting gasification apparatus 10, carbon dioxide and oxygen-containing gas are used to produce reducing gas, which is collected in the region of quenching over the carbon-containing layer, and through the gas pipeline 17 is fed into the recovery reactor with a fluidized bed 8, namely, through the narrowing in the form of a truncated a whisker available in a shaft fluidized bed reduction reactor 8, wherein said narrowing forms a gas distribution bottom 19 and, with the aim of forming a fluidized bed (reduction zone), reducing gas is supplied along the edge of said narrowing using an annular pipe 20.

 Large particles of solids that cannot be maintained suspended in the fluidized bed fall down the center under the action of gravity and are discharged through the central outlet of solids 21. The central outlet of solids 21 is made in such a way that a fluidized stream is formed due to the radial gas feeder 22, which reaches the cylindrical part of the reactor 23, equipped with a conical bottom 24 and located below the gas distribution bottom in the form of a truncated cone 19, so as to ensure satisfactory recovery of large particles.

 Due to the fact that the gas distribution bottom 19 has the shape of a truncated cone, the gas velocity will vary as a function of height. As a result of this, a certain distribution of grain sizes will be established above the level of the gas distribution bottom 19. By appropriately arranging the nozzles in the gas distribution bottom 19, it is possible to form a fluidized bed with internal circulation in which the gas velocity will be higher in the center than at the edges. A fluidized bed structure of this type can be used both in the reduction reactor 8 and in the preheating reactor 1.

 A part of the reducing gas leaving the smelting-gasification apparatus 10 is subjected to purification in a hot cyclone 25 and cooling in a series-connected scrubber 26, after which it is mixed back through the recirculation pipe 28 with a compressor 27 to the reducing gas leaving the smelting-gasification apparatus 10. The dust that is separated in the hot cyclone 25 is transferred back to the melter-gasifier 10 through a gas injector 29. Through a gas feeder 22, which is formed by an annular pipe rovodom Part still uncooled reducing gas discharged from the hot cyclone 25 enters into the reduction reactor 8 fluidized bed through its cylindrical portion 23.

 Through the gas pipe 30, the gas discharged from the reduction fluidized bed reactor 8 is fed to the reduction cyclone 31, in which the fine particles still present in the reducing gas are separated and completely reduced. Through the transport pipe 32 and the gas injector 33, these fine particles are loaded into the melter gasification apparatus 10 at approximately the level of the upper boundary of the layer.

 The partially oxidized reducing gas leaving the recovery cyclone 31 passes through a gas pipe 30 to a preheating reactor 1 with a fluidized bed, but part of it is burned to preheat the reducing gas. The combustion is carried out in a combustion chamber 34, which includes a pipe 35 for supplying oxygen-containing gas.

 Part of the fully recovered feed materials is removed from the recovery reactor 8 with a fluidized bed at the level of the fluidized bed 18 by means of a discharge screw 36 and through the transport pipe 37 and through the gas injector 33 are introduced into the melting and gasification apparatus 10 at approximately the level of the upper boundary of the layer, preferably together with fine particles from a recovery cyclone 31.

 The finely dispersed material separated in the cyclone 4 of the export gas outlet pipe 6 is loaded into the recovery reactor 8 with a fluidized bed through a transport pipe 38 with locks 39 and through an annular pipe 20 for supplying reducing gas. Gateways, similar to gateways 39, are also available in other transport pipelines, such as 9, 32 and 37, designed to transport partially or fully recovered material.

 Installation according to the drawing works as follows.

Prepared, that is, sieved and dried fine ore, is loaded into the preheater 1 pneumatically or using a bag loader or forklift. There it is heated to a temperature of about 850 ^o C in the zone of the fluidized bed 2 and, possibly, partially restored, approximately to the stage of wustite, due to the reducing atmosphere.

For this partial reduction operation, the reducing gas must contain at least 25% CO + H ₂ in order to have sufficient reducing ability.

After this, the preheated and possibly partially reduced fine ore is transferred, preferably by gravity, to the reduction reactor 8, in particular, to the fluidized bed 18, in which the fine ore is mainly reduced to the Fe stage at a temperature of about 850 ^o C. For this reduction operation, the gas must contain at least 68% CO + H ₂ .

 If finely dispersed ore requires a longer recovery time, then a second (and if necessary a third) reduction fluidized bed reactor is installed, including an additional reduction cyclone connected in series with the first reduction reactor 8. In the second reduction reactor, the fine ore is reduced to the wustite stage and in the first reduction reactor 8 to the Fe stage.

Position 40 in the drawing indicates the most important sections of the installation described above, on which the most suitable way can be realized the possibility of connection with a source of CO ₂ and / or a source of H ₂ O, that is, with means for introducing gases containing CO ₂ and / or H ₂ O; the effect of said gases will be described below.

Inlet sections 40 are preferably located either in pipelines 17 connecting the melter-gasification apparatus 10 to the reduction reactor 8, or in the cooling cycle of the reducing gas 26, 27, 28. If the inlet section 40 is located in the cooling cycle of the reducing gas 26, 27, 28 located downstream of the compressor 27, this gives such advantages as, for example, the possibility of using a compressor 27 of a smaller size. In addition, the gas heated by compression will then cool when H ₂ O and / or CO _{2 is} supplied.

 The effectiveness of the measures proposed in accordance with this invention is more fully described in Examples I-IV, where known technology is simply described in Example I. All values presented in the tables of gas composition are given in percent volume.

Example I
The reducing gas produced by a known technology, for example, according to EP-A-0594557, has the composition shown in table I. The reducing gas leaves the melting and gasification apparatus 10 at a temperature of 1050 ^o With a pressure of 4.5 bar abs. It can be used to recover iron ore.

Table I
СО - 65%
H ₂ - 30%
CO ₂ - 1%
H ₂ O - 1%
CH ₄ - 1%
N ₂ - 2%
In order for the temperature of the reducing gas to be about 850 ^{° C.} , cooling gas must be mixed with the reducing gas. In accordance with Example I, cooling gas of the same type is added at a temperature of 70 ^{° C.} , also at a pressure of 4.5 bar abs. To achieve a temperature of 850 ^o With the addition of 27.8% of the cooling gas. This causes the following disadvantages:
- a very large amount of cooling gas is required, since a significant part of the hot reducing gas must be diverted and subjected to cooling operation through the side pipeline, which requires large energy and hardware costs;
- the total content of CO ₂ and H ₂ O does not correspond to the equilibrium, because after adding cooling gas along the way to the reduction reactor 8, strongly exothermic decomposition of CO and H ₂ will occur in accordance with the equation 2CO <--> CO ₂ + C (Boudoir reaction) and СО + Н ₂ <--> Н ₂ О + С (heterogeneous water-gas reaction), respectively. This leads to an increase in temperature, which may require the supply of additional cooling gas. An increase in temperature leads to agglomeration of the material in the reactor. In addition, there is an aggressive chemical effect on metal pipes, built-in elements, etc., with which the reducing gas is in contact. Finally, due to the reaction of CO and H _{2, the} effective amount of gas for reduction is reduced.

Example II
In the reducing gas, which has the composition shown in table I, under a pressure of 4.5 bar abs. introduced a gas enriched in CO ₂ and having a temperature of 70 ^° C. The composition of the gas enriched in CO ₂ is shown in Table II.

Table II
СО - 13%
H ₂ - 2%
CO ₂ - 77%
H ₂ O - 5%
CH ₄ - 1%
N ₂ - 2%
By adding 12.3% of the cooling gas of the same type as in Example I to the reducing gas in Table I and 10.7% of the CO ₂ enriched gas in Table II, a reducing gas was obtained having a temperature of 850 ^{° C.} and a pressure of 4 , 5 bar abs., With a chemical composition according to table III.

Table III
СО - 60.5%
H ₂ - 27.5%
CO ₂ - 7.6%
H ₂ O - 1.4%
CH ₄ - 1.0%
N ₂ - 2.0%
In this reducing gas, the total content of CO ₂ and H ₂ O is close to equilibrium at 850 ^o C, so that the decomposition of CO and H _{2 is} almost completely excluded. The gas enriched in CO ₂ is fed into the cooling gas cycle, for example, into the recirculation pipe 28 in accordance with the drawing. Obviously, in this case, a significant reduction in the size of the cooling gas cycle is possible, since only 12.3% of the cooling gas is required instead of 27.8% in Example I. According to Example II, it is possible to use gases with low calorific value, i.e. gases, enriched with CO ₂ . When reducing iron ore with a reducing gas prepared in this way, excessive heating of the material in the reactor is reliably prevented, and the reduced material can be transferred without problems to the melting-gasification apparatus 10.

 Example III

 In accordance with example II, water vapor is added to the cooling gas of the same type. The chemical composition of the reducing gas leaving the smelting-gasification apparatus 10 and the cooling gas is identical to the chemical compositions shown in example I.

Steam (100% H ₂ O) is added at a temperature of 250 ^o C and a pressure of 12 bar abs. With the addition of 18% cooling gas with 8.5% water vapor, a reducing gas is formed having a temperature of 850 ^{° C.} and a pressure of 4.5 bar abs. The chemical composition of the reducing gas is shown in table IV.

Table IV
СО - 60.7%
H ₂ - 28.0%
CO ₂ - 0.9%
H ₂ O - 7.6%
CH ₄ - 0.9%
N ₂ - 1.9%
This option also provides the advantage of a cycle with small volumes of cooling gas circulation with an almost equilibrium content of CO ₂ and H ₂ O. An additional advantage of this option is a slight change in the number of reducing agents.

Claims (9)

1. A method of producing a hot reducing gas containing CO and H ₂ to recover finely dispersed metal ores, in particular iron ore, by which the reducing gas is obtained in the gasification zone by gasification of carbon carriers, in particular coal, by supplying oxygen, and then cooled to temperature reducing gas which is suitable for the recovery process, characterized in that by introducing H ₂ O and / or CO ₂ to prevent the Boudouard and heterogeneous water-gas reaction, and hence the heating Sun tanovitelnogo gas, reducing gas subjected to cooling without changing the contained H ₂ O and / or CO ₂ is converted into a reducing gas that is thermodynamically stable at the reducing temperature. 2. The method according to p. 1, characterized in that H ₂ O and / or CO ₂ is introduced in amounts that ensure almost complete Boudouard equilibrium and heterogeneous water-gas equilibrium of the reducing gas at a temperature suitable for the reduction process. 3. The method according to p. 1 or 2, characterized in that the input of H ₂ About is carried out by supplying water vapor. 4. The method according to one or more paragraphs. 1-3, characterized in that the input of CO _{2 is} carried out by supplying a gas containing CO ₂ .  5. The method according to p. 3 or 4, characterized in that the reducing gas serves reducing gas that has reacted in the recovery process. 6. The method according to one or more paragraphs. 1-5, characterized in that the cooled gas of the same type is mixed with the reducing gas, and H ₂ O and / or CO ₂ are introduced into the cooled reducing gas. 7. Installation for implementing the method according to one or more paragraphs. 1-6, comprising at least one recovery reactor (8) with a conveyor pipe (7) for metal ore included in it and a reducing gas pipeline (17), including a gasification reactor (10) with feed pipelines included (11) 12) for carbon carriers and oxygen-containing gases and exiting therefrom conduit of reducing gas (17), and further comprising cooling means arranged in the conduit of the reducing gas (17) and does not affect the content of H ₂ O / CO ₂ to the reducing gas, of Leach in that the reducing gas to the conduit (17) for feeding the cooled reducing gas is connected (coupled) a source of CO ₂ and H ₂ O. source  8. Installation according to claim 7, characterized in that the reduction reactor (8) is equipped with a blast furnace gas outlet pipe (6, 30) for discharging the reacted reducing gas, from which a side pipeline (41) connected to the reducing gas pipeline (17) is branched . 9. Installation according to claim 7 or 8, characterized in that the recirculation gas pipe (28) is removed from the reducing gas pipeline (17), which is again connected to the reducing gas pipe through the scrubber (26) and compressor (27) at a point located above the branch point of the recycle gas recovery pipe (28) relative to the direction of flow of the reducing gas, in particular above the dedusting device (25) available on the recovery gas pipe (17), and that the source C O ₂ and / or a source of H ₂ O are connected to the recirculation pipe of the reducing gas (28).

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